1. Field of the Invention
The present invention relates to a satellite positioning apparatus for use in a satellite positioning system, such as the global positioning system (GPS), for determining the position of the apparatus based on signals received from satellites.
2. Description of the Related Art
GPS is a well-known satellite navigation system including a plurality of satellites and a satellite positioning apparatus that moves along with a mobile object, e.g., a vehicle.
One known positioning technique for use in GPS receivers serving as such GPS satellite positioning apparatuses is positioning with the use of only signals received from high-elevation satellites, thereby reducing multipath effects on the positioning accuracy, which are caused by obstacles, such as buildings (see, for example, Japanese Unexamined Patent Application Publication No. 6-281721).
Another known positioning technique for use in GPS receivers is positioning with the use of signals received from a group of satellites providing the best DOP (Dilution of Precision) that is determined from satellites from which the GPS receivers can receive signals (see, for example, Japanese Unexamined Patent Application Publication No. 5-297104). DOP is a measure of the geometrical strength of the satellite configuration.
The positioning accuracy and error of a satellite positioning apparatus vary depending upon a combination of satellites used for positioning. Frequent changes of the satellites used for positioning can deteriorate the positioning stability of satellite navigation, and can cause position jumps or positioning errors. Such position jumps or positioning errors make it difficult to correct the position determined by the satellite navigation apparatus to a correct position using a correction technique, e.g., map matching between a trajectory defined by determined position records and a road map view.